Audio production for television, video, film, and recorded music sales is a large and growing enterprise, and is the foundation of much of the entertainment industry. Automation in the form of computerization is becoming more and more important as the basis of technical advances in this industry, to provide ability to mix and process more sophisticated and more voluminous audio input, and to provide more flexibility in output. Computerization is also seen as a requirement for cost-effective competition. Manual instruments, systems, and techniques are, by comparison, increasingly more expensive to use.
The basic instrument of audio production is the production mixing console, a workstation presenting an interface to a sound engineer through which he or she may condition multiple channels of audio input, and mix the conditioned results into mono or stereo outputs for direct broadcast or for recording. A production mixing console, hereinafter a mixer, typically presents arrays of input devices, such as switches, knobs, and "faders", for an engineer to set to condition and route audio signals. A fader is typically a slide rheostat through which an amplitude may be adjusted as a result of the linear position of the input lever relative to a track.
Mixers typically route audio input signals to individual channels, and each such channel has a repetitive layout of switches, knobs, and faders. For example, a single channel can have more than one input, such as a microphone input and an input from an instrument, a group of instruments, or a tape. Using the controls on a mixer an engineer can select microphone, line, and tape inputs, route the inputs to signal conditioning devices like faders and equalizers, and mix and route the output from the conditioning devices as well. There is typically a selective ability to monitor audio signals, such as by headphones, and often a microphone for talkback by the sound engineer operating the console.
Audio mixing, especially with digital techniques and computer control, is historically a rather recent development. When rock-and-roll music was first introduced there was no such device as a mixer. In the fifties, recording was done by direct input. Modern mixing was initiated about the time of the appearance of the Beatles, and the first units were highly individualistic. Through the sixties and early seventies direct audio mixers continued to be developed, and continued to be relatively small units with a few channels and were very unique in layout. In the mid-seventies standards began to appear, especially relative to layout of switches, rotary potentiometers, and faders. With a standard layout it became possible for a sound engineer to go from one studio to another, and take over the functions comfortably.
In the early development and well into the late seventies, mixers were completely manual. The audio signals were routed to the mixer, and directly through the switches, pots, and faders. As a result, there were some definite limitations and problems. For example, with the audio signals routed directly through the switching and signal processing devices, it was necessary that heavy duty, low noise devices be developed. Without ultra-high quality devices, contacts, rheostat slides, and the like produce unwanted clicks and other noises that are incorporated into the audio signals.
In answer to some of the problems of direct-audio mixing consoles, some manufacturers have developed digital systems, wherein the input devices on the console do not directly control audio processing equipment, but instead provide digital input, which may be manipulated and saved by the system, and used indirectly to control other devices that process audio signals.
FIG. 1 is an isometric view of a system 11 developed by Euphonix, Inc. of Palo Alto, Calif. for applying the power of digital techniques to audio processing and mixing. In this system console 13 is almost entirely digital, and all audio processing is accomplished in an audio tower 15.
FIG. 2 is an illustration of a pattern 17 of input devices, such as knobs, slide rheostats, and so forth, on the front panel of the console of FIG. 1. The purpose of FIG. 2 is to illustrate the density of input devices and position indicators, which pretty much cover the console surface, being arranged in channels and blocks of like devices. These input devices provide digital position signals which are manipulated and stored, and used to compose and send digital signals to digitally controllable audio processing and mixing devices in the audio tower.
The move to digital systems has provided a very important feature for audio engineers, that was simply not before available. When an engineer has a console set for a particular purpose, say a particular musical group doing a particular sort of music, he or she invariably encounters the situation where a previous complete setting is desired. Before the advent of digital systems, the only answer was to make notes, mental and otherwise, of settings, and then reset all of the input devices on the board from memory and the notes.
With the advent of digital systems, a computer associated with the system can remember the setting of every knob, slide switch, and pushbutton. It is only necessary to provide a signal to store all current settings (often called a "snapshot" in the art). Then, at a later time, another signal can retrieve the previous settings from memory storage. The way the computerized system "gives back" the information, though, presents new problems in the art.
One difficulty is related to the nature of the digital input devices, particularly knobs. In conventional, directly-coupled systems, knobs operate rotary potentiometers. An example is a one-turn pot. The pot had a minimum and a maximum input setting, and could be set at any position in between, the resistance of the pot being proportional to the setting position setting. in a digital system a knob is typically sensed by a shaft encoder, and the "real" setting is determined by recording the amount of rotary movement from an assigned base, or zero, position. Such a rotary input can correctly be called an infinite knob, in that there is no minimum or maximum physical setting. A new base position may be assigned at any time. Likewise, a new position relative to "zero" may be assigned at any time.
FIG. 3 is a block diagram illustrating the general situation with a series of digital input knobs 19, 21, and 23, representing a set of knobs 1-n. Shaft encoders 25, 27, and 29 respectively "read" the rotation of knobs 19, 21, and 23, and present the magnitude and direction of rotary movement to a CPU 31, configured to calculate and store values in a series of operating registers 33 in RAM 39. The values in operating registers 33 are used by the digital system to drive signal processors that actually alter and mix the audio signals input to the system. It will be apparent to one with skill in the art, as well, that there may be multiple processors, various kinds of bus devices such as bus 30, and other arrangements of digital elements for computation and communication, which are known in the art.
The encoders read discrete increments of rotary motion in some number of increments of revolution, the greater the number the greater the resolution. For example, a particular encoder may be configured to report 256 increments per revolution.
The setting for each knob is determined in operating registers 33 by adding and subtracting the discrete increments of rotation. A setting (snapshot) of the series of knobs 1-n is made on signal by the engineer operating the board by storing the immediate value of operating registers 33 in another series of registers 35 for later retrieval and use, and then continuing to update the immediate registers. Any number of snapshots may be made and stored, depending on the configuration of the system, in separate memory register locations, with the snapshots having names or numbers for identification in retrieval.
In the digital system, when one wishes to retrieve a snapshot, to set up the board according to a previously stored global setting, a signal is given with the name or number of the snapshot to be restored, and the stored setting (such as the values in registers 35) is retrieved and substituted for the values in operating registers 33.
Once an engineer recalls a setting, and all of the operating registers are reset to the recalled value, representing knob positions, the idea is to proceed from that point making new adjustments in the settings to account for changing situations and conditions, but now a serious problem emerges.
The problem is, that in the older, directly-coupled system, there were absolute minimum and maximum positions. A knob, then, could be imprinted with an indicator line or arrow to align with an indicator on the panel, to tell an engineer at a glance the absolute setting. The knobs in the digital case are not directly coupled, however, and the recalling of a setting provides the desired operating values in the operating registers, but does nothing to indicate a relative knob position. The knobs are not reset, so the engineer is deprived of critical feedback.
There are several ways this problem might be solved. One solution known to the inventors is to have absolute indicators on the knobs and the panel, and to provide motor drives for the knobs, so when a snapshot is recalled, the recalled values are used to operate the motors to drive the knobs to the recalled setting. Then the engineer can operate the board from the new position just as is done in the older, directly-coupled systems.
Considering the density of operating devices as shown in FIG. 2, one can easily understand the difficulty of the motor-drive solution. The motor drives are relatively bulky, the drives are expensive, having to be coupled in a manner, such as by clutches, to allow manual movement of the knobs after resetting, and the density of control and power wiring behind the panel is typically more than doubled. Heat generation is increased, and system reliability is adversely affected.
Another possible solution is shown in FIG. 4A. In this case, knob 37 has a series of built-in LEDs, such as LED 40, around the periphery, and an absolute indicator 41 on the panel. When a snapshot is recalled, the new setting value is used to light the one appropriate LED in the knob that most closely shows the new setting relative to absolute indicator 41. If the recalled value for this particular knob indicates 50% of full value, for example, the system will light LED 43, 180 degrees from the absolute indicator. The knob is then effectively "reset" just as though driven to a new position by a motor. The engineer knows which direction of rotation increases setting value, so that is not a problem.
The LEDs in the knob solution suffers from the density problem as well. The panel density dictates that knobs are relatively small, and there is a low limit to the number of LEDs that may be installed in one knob, providing poor resolution. Also, there is the problem of selectively lighting the LEDs in the rotary knob.
FIG. 4B shows a variation of the solution of FIG. 4A. In this case, knob 45 has an absolute indicator 47, and the LEDs are arranged in a circle around the knob, such as LED 49. When a setting is recalled, the appropriate LED is lighted indicating the setting. For example, if the recalled setting is 50% of full value, LED 51 may be lighted.
The solution of FIG. 4B relieves the resolution problem of that of FIG. 4A, but not by much. In addition, there must be some reliable means of keeping track of the absolute position of knob 45, and the recalled settings force the engineer to operate from a new absolute position after each recall.
What is needed is a means of providing the new setting positions to the engineer quickly and reliably without sacrificing resolution or increasing wiring density and complexity.